Cleanrooms and other environments in which contamination is to be controlled have special requirements for the materials to be used therein. Of paramount concern is the generation of particulate contamination. It is well known that particulates can be brought into the cleanroom environment by workers themselves and by the materials which they use. In this regard, items which are subject to abrasion or wear are a cause of special concern.
Cleanrooms are characterized by a special emphasis on the prevention of particulate generation and the removal thereof prior to deposition on cleanroom surfaces and products to avoid re-entry into the air at a later time. To that end, large volumes of air are flowed through the room, typically in a nested fashion, such that particles released into the cleanroom atmosphere will be quickly swept away. Structures which impede this process are either modified or eliminated. For example, gratings are substituted for solid shelving. In addition, dust generators such as paper or boxes are strictly for precluded from entry. In another effort eliminating particulate generation, the workers are clothed in special garments which not only contain the debris generated from the human body, hut also are themselves resistant to particulate generation as a result of abrasion or wear.
It has long been recognized that fabrics are subject to fraying regardless of construction. Not only will the woven or knit fibers or filaments unravel, that is separate one from another, but the filaments are subject to material damage from both the cutting process in cloth fabrication and by subsequent use in the cleanroom. For cleanroom applications, the fabrics typically chosen include a high percentage of thermoplastic fibers, such as polyester, nylon, polypropylene and other related thermoplastic fibers and yarns, and are either of Woven or knit construction.
Cleanroom garments and wipers have most recently incorporated edge treatment to control fraying. Known edge treatments include a hem wherein a portion of the edge is folded back onto itself and into the body of the material to encapsulate the edge within a portion of the fabric material. This approach is effective in reducing particulate contamination, but requires expensive processing of the garment or wiper.
For thermoplastic materials an edge ca be treated by heat to fuse a portion of the area at the edge and a margin adjacent thereto. Techniques for fusing edges and creating a boundary include the woven textile fabric and method and apparatus for making the same in U.S. Pat. No. 4,534,819. Disclosed therein is a woven textile fabric with at least 65% thermoplastic fibers having an edge which is ultrasonically sealed and cut to prevent the fraying of the edge. Fabric made in accordance with the '819 invention has a border extending inward from the edge of between 1/100th to 1/10th of an inch to encompass between 2 and 4 of either of the warp or filing yarns which extend parallel to the cut edge.
U.S. Pat. Nos. 4,560,427 and 4,610,750 disclose ultrasonic seal and cut methods and apparatus for sealing and cutting fabric having thermoplastic filaments. The '427 and '750 techniques generate a sealed marginal area extending backward into the fabric from the edge. The prior art also includes U.S. Pat. No. 3,087,846 which discloses a method of trimming an edge sealing textile fabrics. The '846 method incorporates a hot wire device which knives through a piece of thermoplastic fabric. The '846 method cuts the fabric, creating opposed edges in two subpieces. The '846 method includes sealing simply the immediate edges as well as melting or fusing a portion of the marginal areas surrounding the edges to create a fused border extending into the fabric a distance of 1/4 of an inch.
U.S. Pat. No. 4,888,229 discloses a wiper for use in a cleanroom. The '229 wiper includes thermoplastic material having a fused border around the peripheral edges. The '229 wiper is made from a sheet of fabric having thermoplastic material knit or woven therein. The '229 wiper is fabricated by fusing regions within a fabric sheet of indeterminate size, thereafter, the individual wipers are cut from one another. wipers made in accordance with the '229 method are fabricated from individual sheets which can be combined thereafter to create a wiper of one or more plys. Multi-ply wipers made from individual sheets require that the several plys be registered with one another prior to the generation of a fused border or marginal region.
Characteristic of the '229 wiper is fused border around the entire wiper periphery since the wiper is made from a fabric sheet. Sheets are formed, for example, by slitting a knit fabric tube in a longitudinal direction. Therefore each edge in a wiper will incorporate a cut edqe and will need edge treatment. Fused borders are also undesirable in that they are subject to failure unless they extend into the wiper a substantial distance i.e. approximately 3/10 of an inch. The ahrasiveness of the fused portion is likewise undesirahle.
It would be advantageous to have a wiper for use in a cleanroom which is inexpensive to manufacture and has only a limited number of cut or free edges which require modification. The present invention is drawn towards such a wiper.